Method for determining liquid-vapor interface via gamma radiation

1. A method for determining the position of a liquid interface between a lower tray and an upper tray in a process apparatus comprising the steps of:

a) arranging a source of gamma radiation and a detector for said gamma radiation at opposed ends of a horizontal path P through said process apparatus, said path P being located at a vertical location between the height of said lower and upper trays and at height H above said lower tray;

b) counting the amount of radiation emitted by the source which is detected by the detector;

c) carrying out steps a) and b) N times to acquire N data points Dn, each consisting of the count rate Cn counted by the detector measuring radiation transmitted along path Pn at height Hn above said lower tray, each path Pn being of the same length and H 1 being at or immediately above the height of the lower tray;

d) defining the count rate CV to be the count rate when the path through the process apparatus passes through a vapour phase;

e) identifying C MAX where C MAX =the maximum of measured count rates Cn between said lower tray and said upper tray; and

f) estimating the height H L of the liquid interface by:—

i. if C MAX ≦CV and C MAX ≧CV−x % of CV then H L =Hn at C MAX ; or

ii. if C MAX <CV−x % of CV then extrapolate data points, including Dn at C MAX and at least Dn−1 and Dn−2, to find H L where extrapolated line meets CV.

2. A method according to claim 1 wherein, if more than one count rate fulfils the condition in paragraph f) i, then H L may be taken to be at the lowest height Hn, at which the condition is fulfilled.

3. A method according to claim 1 , further comprising the step of calculating the liquid interface position from H L and the position of the lower tray.

4. A method according to claim 1 , wherein N is at least 5.

5. A method according to claim 1 , wherein the count rate is expressed as log 10 (count rate) and step ii of part f) is carried out using a straight line fitting method.

6. A method according to claim 1 , wherein the calculated liquid height, H L , is used to calculate the % flood by expressing H L as a percentage of the distance between the lower tray and the upper tray.

7. A method according to claim 1 , further comprising the step of adjusting the operating parameters of the process apparatus based on the value of H L estimated in step f).

8. A method according to claim 1 , wherein x is between 1 and 15.

9. A method according to claim 1 , wherein said process apparatus is a distillation column.

10. A method according to claim 2 , further comprising the step of calculating the liquid interface position from H L and the position of the lower tray.

11. A method according to claim 2 , wherein N is at least 5.

12. A method according to claim 2 , wherein the count rate is expressed as log 10 (count rate) and step ii of part f) is carried out using a straight line fitting method.

13. A method according to claim 3 , wherein the count rate is expressed as log 10 (count rate) and step ii of part f) is carried out using a straight line fitting method.

14. A method according to claim 2 , wherein the calculated liquid height, H L , is used to calculate the % flood by expressing H L as a percentage of the distance between the lower tray and the upper tray.

15. A method according to claim 2 , further comprising the step of adjusting the operating parameters of the process apparatus based on the value of H L estimated in step f).

16. A method according to claim 2 , wherein x is between 1 and 15.

17. A method according to claim 2 , wherein said process apparatus is a distillation column.